I. Field of the Invention
The present invention relates to antenna technology. More particularly, the present invention relates to a novel and improved dielectric lens antenna.
II. Description of the Related Art
Wireless communication systems are playing an increasingly important role in contemporary society. An integral and important component of any wireless communication system is the antenna. Antennas in a wireless communication system provide a region of transition between a guided wave and a free space wave. Antennas are used as both a transmitting device and a receiving device.
In order to increase the performance of the communication systems, antennas are designed to radiate (or receive) energy as effectively as possible. One measure of the effectiveness of the antenna is its gain. One way to increase the gain of an antenna is to increase the antenna""s directivity. However, with directional antennas, the increase in gain is in a preferred direction and is typically obtained at the expense of gain in other directions. Thus, while directional antennas provide increased gain in the preferred direction, unless the antenna is pointed at the target (or source) with a fair degree of accuracy, the antenna is not being utilized effectively.
To take advantage of an antenna""s directivity, systems which utilize directional antennas typically also include a mechanism for pointing the antenna such that the antenna""s main lobe is pointed at the target (or source). In systems where the relative positions of the source and target change over time, a mechanism for steering the directional antenna is often utilized.
For example, a satellite ground terminal or earth station typically utilizes highly directional dish antennas to communicate with one or more orbiting satellites. High directivity and high gains are achieved by utilizing dishes having diameters anywhere from several centimeters in diameter to several hundred meters in diameter. Because such antennas are highly directional, they must be pointed at the satellite with a great amount of accuracy.
To achieve this pointing accuracy, expensive and complex antenna mounts are utilized. These mounts are typically one of two types: x-y mounts and azimuth-elevation (az-el) mounts. Both types of mount require a pointing algorithm to determine the desired direction for the antenna and a motor and motor control system to steer the antenna to the desired position. Such antenna mounts and their associated motor and motor control systems are mechanical in nature and utilize moving parts. As such, regular maintenance and upkeep of such systems is required, and the systems are subject to failure.
The use of steerable antenna mounts is not limited to dish antennas at satellite earth stations. Indeed, there are numerous other applications where it is desirable to steer an antenna (dish or otherwise) to a target (source). In most conventional applications, as with the satellite-dish application described above, the antenna pointing/steering systems are mechanical in nature and utilize moving parts. As such, these systems are also subject to the same maintenance and upkeep concerns as the satellite-dish systems. In addition, their relative speed in changing directions using mechanical drivers may be slower than desired for some applications.
Another technique used to increase the gain of an antenna is to focus the energy using a dielectric lens. Dielectric lenses are typically fabricated by shaping a dielectric material having an index of refraction xcex70, where xcex70 is greater than one. Dielectric lenses have been used in communication and radar systems to focus electromagnetic waves and to adjust the aperture of an antenna. The operation of a dielectric lens with electromagnetic waves at radio and microwave frequencies is analogous to the operation of optical lenses in an optical system. One common use of a dielectric lens is to convert a signal having a spherical phase front to one having a planar phase front, thus, focusing the radiation into a narrow beam.
The present invention is a novel and improved dielectric lens assembly. According to the invention, an extension of length L is included on a hemispherical dielectric lens to provide a dielectric lens which exhibits properties of an elliptical lens. The extended dielectric lens can be implemented with a feed antenna, such as, for example, a slotline antenna or a spiral antenna, to improve the directivity of the antenna.
In one embodiment, the extension portion of the lens assembly is fabricated using a plurality of dielectric substrates or plates. The substrates are disposed on the bottom surface of the hemisphere to allow the feed antenna to be positioned at a distance L from the center of the sphere described by the hemispherical dielectric. Preferably, the position of the feed antenna on the extension is coincident with the focus of an ellipse synthesized by the combination of the hemispherical lens and extension.
The extension can be made of the same dielectric material as the lens, or of alternative dielectric materials. Where alternative dielectric materials are used, it may be desirable to use a matching layer at the hemisphere/extension interface.
The entire hemispherical lens and extension assembly can be a single piece of dielectric material formed into the desired shape, or the assembly can be fabricated using a plurality of dielectric components coupled together to form the lens assembly.
In one embodiment, the extension is roughly cylindrical in shape. In alternative embodiments, the extension is of an alternative shape suitable for positioning the feed antenna at the focus of the synthesized ellipse.
In yet additional alternative embodiments, the extension portion of the lens assembly is angled to allow the feed antenna to be positioned off axis, while maintaining a roughly constant extension length L. With the angled extension embodiment, one or more planar surfaces are provided on the extension.. The distance from a point on the planar surface through the center of the sphere described by the hemisphere to the aperture surface of the hemispherical lens is within a range of lengths for which the directivity of the signal is above a threshold level, from any point along the surface.
In yet another alternative embodiment, the extension portion of the lens assembly is hemispherical and preferably has a radius equal to an optimum extension length L. Because the radius is equal to the optimum extension length L, the feed antenna can be positioned anywhere on the surface of the extension while maintaining optimum directivity. As such, antenna pointing by positioning or selecting an antenna at a point on the surface can be accomplished while maintaining optimum directivity.
In one embodiment, the dielectric lens assembly is implemented in conjunction with an objective lens to enable coupling of the antenna with another system.
Although this document utilizes the word xe2x80x9cplanarxe2x80x9d to describe the one or more surfaces of the angled extension, it is not intended to limit the configuration of the surface to that of a perfectly planar surface. As would be understood by one of ordinary skill in the art after reading this description, the planar surface need only be xe2x80x9cperfectxe2x80x9d enough to provide a suitable mounting surface for the planar antenna used in the preferred embodiment. Thus, the planar surface can be merely approximately planar. Additionally, as understood by one of ordinary skill in the antenna art, a xe2x80x9cplanar antennaxe2x80x9d is also not necessarily perfectly planar.